The present invention relates to a power audio-amplifier provided with the capability of automatic adjustment of the bias current absorbed by the final stage.
It is known that power audio-amplifiers are affected by "cross-over" distortions, from which troublesome noises can result, particularly in case of radio transmissions.
It is likewise known that such distortions can be avoided by keeping the bias current absorbed by the final stage, also called the rest-current, at a relatively high value such as 10.div.15 mA.
Such current, if it can be accepted in the normal load condition is excessive in the no-load condition, particularly if the current is provided by a battery and the amplifier is destined to be contained in a rather small casing. In such case, the high bias current absorbed during the no-load condition, on one hand causes the quick discharge of the battery and, on the other hand creates an undesirable heat dissipation.
On the other hand, as has already been said, more limited bias currents, as for example 1 mA, would not run down the battery and would dissipate much less heat, but during the load condition would originate the above described "cross-over" phenomena.
Considering this, the object of the present invention is to realize a power audio-amplifier, which is able to combine the two needs of avoiding "cross-over" phenomena during the load working and limiting the run down of the battery and the heat dissipation during the no-load working.